Summary Avitec Tractor 197 was towing an Air Transat AirbusA310 aircraft from Terminal3 on the east side of Toronto/LesterB. Pearson International Airport to the central de-icing facility on the west side of Runway15L. The tractor driver had received and acknowledged authorization to tow via taxiway Sierra (which crosses Runway15L) and taxiway Echo, to hold short of taxiway Tango. At the same time, Air Canada Flight757, a Boeing767-200 aircraft, was cleared to position on Runway15L. A minute and a half later, Flight757 was cleared for take-off. At that moment Tractor197 was crossing the hold line on taxiway Sierra, proceeding to cross Runway 15L in accordance with his authorization. The tractor driver saw Flight757 in position on the runway but did not perceive it to be in motion until he was fully onto the runway and in a position where he had no alternative but to continue to cross in order to vacate the runway as quickly as possible. After commencing their take-off, the flight crew of Flight757 observed the tractor and tow entering the runway. They rejected the take-off, reaching a speed in excess of 90knots approximately 2500feet down the runway, 3500feet from taxiway Sierra. When Tractor197 cleared the runway, the aircraft had slowed to less than 40knots and was 1000feet from taxiway Sierra. Flight757 cleared the runway at taxiway Sierra. Ce rapport est galement disponible en franais. Other Factual Information On the morning of the occurrence, the airport started operations using Runway05 for departures and Runway06L for arrivals. During the two hours prior to the occurrence, visibility had been 10to 12statute miles, the ceiling 5300feet, and winds generally 120M at 8to 9knots. There had been a brief, very light rain shower at 0738 eastern daylight time1, just over two hours before the occurrence, during which the winds were 130M at 10knots with gusts to 15knots. The use of Runway05 was consistent with the Toronto/LesterB. Pearson International Airport (LBPIA) preferential runway policy, which favours the use of 05/06L (or the reciprocals) up to a crosswind component of 15knots for wet runways and 25knots for dry runways. Thunderstorms northwest of Toronto caused departure restrictions and delays for aircraft flying to the northwest. About 30minutes before the occurrence, a tailwind of 25knots at 400feet above ground level (agl) was reported for departures off Runway05. Ten minutes later, the winds at 2000feet agl were reported to be 250 at 50knots, and departing flights began to refuse Runway05. The departure runway was changed to Runway15L approximately 10minutes before the occurrence. Flight757 was the fourth aircraft to depart from Runway15L. At the time of the occurrence, the tower was staffed by a tower supervisor, a tower controller in the South Tower, an on-job trainee (OJT) and an on-job instructor (OJI) in the North Tower position, two ground controllers (north and south ground), and a clearance delivery controller. There is provision for a centre ground controller, but it was not staffed. Tower staffing was consistent with NAV CANADA policy and the controllers were properly qualified for their functions. Shift schedules the preceding day and breaks on the morning of the occurrence were also consistent with NAV CANADA policy. With the exception of the north ground controller, air traffic control (ATC) workload was neither heavy nor complex. The north ground controller had a heavy workload, though not complex. The runway change, 10minutes prior to the occurrence, had necessitated amending the departure clearances for most aircraft. In addition, aircraft affected by departure restrictions to the northwest had to be re-sequenced. At 0939:12, Tractor 197 requested clearance from the Terminal3 apron to the central de-icing facility. The north ground controller issued authorization that implicitly included clearance across Runway15L, the active departure runway. He did not co-ordinate the movement of Tractor197 with the north tower controller. After ensuring that Tractor197 understood his sequencing behind a taxiing DHC-8 aircraft, the north ground controller was occupied with other taxiing aircraft and with entering data into the extended computer display system (EXCDS). He was unaware of the conflict until he was alerted to the incursion by the clearance delivery controller. At 0939:08, after clearing the aircraft ahead for take-off, the north tower OJT cleared Flight757 to position on Runway15L and at 0940:40, cleared it for take-off. The OJT had scanned the runway before issuing the clearance but did not notice Tractor197, which at the time was approaching the hold line on taxiway Sierra. The OJI also scanned the runway prior to the take-off clearance being issued; he saw Tractor197 and assumed that it would hold short. While Flight757 was on the take-off run, both controllers looked away from the runway to glance at the weather display on the enhanced traffic management system (ETMS) monitor. As the OJI returned his attention to the runway, he saw the crossing tractor and tow at the same time as the clearance delivery controller spoke. The first indication of the incursion to ATC controllers in the tower came from the clearance delivery controller, whose position had him facing almost directly toward taxiway Sierra. He happened to glance outside and notice Tractor197 entering the runway while Flight757 was on its take-off run. He shouted a warning to alert the tower and ground controllers to the conflict. Realizing that continuing across the runway was the most expeditious way for Tractor197 to get clear, the north ground controller decided not to intervene. The north tower OJI instructed Flight757 flight crew to abort the take-off, but they had already begun to reject the take-off and had already made a transmission to that effect to the tower. The day before the occurrence, the north ground controller requested and was allowed to leave early because of his mother's illness and admission to hospital. The next day, understanding the staffing level to be adequate but not sufficiently flexible to easily accommodate an unplanned absence, he came to work at approximately 0545 for his normal shift. He did not indicate any duress to the tower supervisor and he handled a heavy workload and performed his duties competently during the time leading up to the occurrence. The north ground controller was aware that the active runway had been changed to Runway15L. He had issued amended clearances to several aircraft and had seen the first three aircraft depart from that runway. A ramp hold had been imposed earlier while the decision was being taken to change the runway, but it had been lifted by the time of the occurrence. The north ground controller had approximately 10aircraft, three ground vehicles, and Tractor197 under his control. One aircraft was inbound to Terminal3 and was being held on taxiway Alpha between Terminal1 and Terminal3 until Tractor197 could be cleared out of his route. The driver of Tractor197 was properly qualified under the Greater Toronto Airport Authority (GTAA) airside vehicle operator (AVOP) program. He had been on duty since midnight, but since he had no calls, he had slept during the night and was well rested. After receiving authorization from the north ground controller to proceed to a point on the other side of Runway15L, the driver was under no obligation to obtain further clearance to cross the runway and he believed his task was to comply fully and promptly. It was not abnormal to see an aircraft lined up on the runway, and he did not perceive any motion nor did he notice any lights on the aircraft until after he entered the runway. He continued to clear the runway as expeditiously as possible although he was already near the maximum speed at which he could tow. When Flight 757 was cleared to position, the flight crew turned on their strobe lights and landing lights while they taxied onto the runway. The aircraft under tow had not crossed the hold line when Flight757 was cleared for take-off. During the initial part of the take-off run, the attention of both pilots was partly directed inside the cockpit. The first officer was first to notice the tractor-plus-tow. Initially, he expected the tractor to stop short of the runway and it took a few seconds before it was apparent that it was not going to stop. The first officer then alerted the captain and they rejected the take-off. Toronto/LBPIA is equipped with airport surface detection equipment (ASDE) that provides a real-time display of aircraft and other traffic operating on airport manoeuvring areas. It was operating on the day of the occurrence but was not used by the north ground controller nor was it required that it be used in controlling ground traffic. The Toronto/LBPIA ASDE system is equipped with a feature known as runway incursion monitor/collision avoidance system (RIMCAS), a software enhancement that is intended to provide an alarm in advance of potential conflicts on the runway so that avoidance action can be taken. It does not rely on visual detection, which may not be effective in night or instrument flight rules (IFR) conditions. At the time of the occurrence, the RIMCAS was not on, nor was it required to be as it was not yet commissioned and was used only selectively while false alarm problems were being addressed. It has since been commissioned for operational use after some minor changes to software. The preferential runway system at Toronto/LBPIA calls for use of Runways05/23 and 06L/24R, subject to wind and surface contamination limits, for capacity maximization and noise abatement purposes. When Runways15L and15R are active, Runway15L is usually used for take-offs due to GTAA noise abatement procedures2. Capacity limitations inherent in the Runway15 operation result in a greater than normal backlog of departing traffic, congesting taxiways parallel to Runway15L. In this scenario, the north ground controller usually handles aircraft taxiing for departure. That was the situation at the time of the occurrence. The main terminals are east of Runway15L, and the central de-icing facility, and a growing amount of infield ramp facilities are to the west. There is a heavy volume of ground traffic crossing Runway15L/33R at all times. This ground traffic is also the responsibility of the north ground controller. The control tower at Toronto/LBPIA has provision for a third ground controller (centreground), intended to relieve workload on the other two ground controllers, typically in adverse weather conditions or when the de-icing facility is in operation. The centre ground controller position was not in operation on the day of the occurrence, nor was it required to be in operation. Taxiway entrances to Runway15L/33R are equipped with a stop bar lighting system for use during low-visibility operations on Runway33R. The stop bar lighting is controlled by the appropriate tower controller. It can only be selected in conjunction with lighting for Runway33R and cannot be turned on from the Runway15L control screen. Visibility at the time of the occurrence was good and did not require adherence to low-visibility procedures; i. e., the stop bar lighting was not turned on, nor was it required to be turned on. Runway incursions have been recognized as a worldwide problem for some years. In July1999, the Transport Canada National Civil Aviation Safety Committee (NCASC) formed a sub-committee on runway incursions (SCRI) to develop a national strategy. NAV CANADA undertook a parallel study. The studies shared some common meetings with the aviation community and a panel of experts to review the data. According to the Transport Canada SCRI final report3: traffic volume, capacity-enhancing procedures, and aerodrome layout have been shown to increase the potential for a runway incursion . . . [but] human error is the mechanism . . . in an actual occurrence; and, the majority of Canadian runway incursions are associated with pilot errors. The report recommended that, Transport Canada focus on developing preventive strategies for runway incursions that result from pilot deviations . . . . It also recommended, inter alia, that: 4.5 Transport Canada require that an explicit ATC clearance be given for an aircraft to cross any runway. 4.6 Transport Canada ensure that existing line up and wait procedures are revised to preclude aircraft from being positioned on an active runway if a take-off delay is anticipated. 4.9 Transport Canada develop and implement common standards and recommended practices (CAR322) for all Canadian aerodromes. 4.11 In consultation with airport authorities, Transport Canada investigate the viability of an automated runway incursion warning system, using inductive loop or similar technology, that provides a direct warning of an approaching hold line to the pilot. Transport Canada has formed an incursion prevention action team (IPAT) to oversee the implementation of the common recommendations of these studies and to develop an awareness program. The awareness program commenced with an article in the Aviation Safety Letter4 issued in October2001. The article summarized the analysis contained in the Transport Canada report, stated that 23recommendations were made in the Transport Canada study and 27recommendations in the NAV CANADA study, and that many of the recommendations . . . have been . . . or are being implemented. Specific preventive measures were not identified, and there is no document or statement indicating the status of recommendations - whether they have been accepted or not, or what implementation action is planned. On 04 October 2001, Aeronautical Information Publication (AIP) section RAC4.2.5 was amended to require pilots to hold short of any runway until obtaining a specific clearance to cross; and to emphasize the pilot's obligation to acknowledge instructions to hold short while taxiing either by reading back the clearance or by repeating the hold point, except that read-back is not required in the case of a hold short issued with respect to communications transfer. A Transport Canada Aviation Safety Letter5 issued January2002 continued the awareness campaign with an article by NAV CANADA. It outlined the problem, gave examples of runway incursion accidents, and indicated steps being taken by NAV CANADA to address issues within its control. It mentioned that the requirement for pilots to read back hold-short instructions was a result of a recommendation in a1987 Canadian Aviation Safety Board special investigation. The procedural change, requiring pilots to hold short of any runway until obtaining a specific clearance to cross, was not mentioned in this article nor was it publicized by other facets of the safety promotional campaign. On 10 October 2001, Transport Canada issued an Aerodrome Safety Circular6 indicating that Aerodrome Safety was considering the strengthening regulatory requirements for, inter alia, procedures for access and control of vehicles and that other initiatives may be addressed in the future development of part302 of the Canadian Aviation Regulations (CARs) and standard3227 of the CARs. CAR302 presently requires airside vehicle operations to be controlled by the individual airport's operations manual in accordance with the applicable standards set out in the aerodrome standards and recommended practices publications as they read on the date on which the airport certificate was issued . . . . Aerodrome standards and recommended practices are published in Transport Canada TP312, Aerodrome Standards and Recommended Practices: the most recent version was issued in March19938. It requires that vehicles be operated on manoeuvring areas only as authorized by the air traffic service unit . . . It contains no specific direction to the driver, equivalent to the instruction provided to pilots in AIP section RAC4.2.5, as to the instruction needing to be specific, nor does it explicitly instruct the driver to stop and hold short in the absence of a specific authorization. The driver of Tractor 197 obtained authorization to proceed from the air traffic service unit. He did not receive, nor did the Aerodrome Standards and Recommended Practices require him to receive, an explicit clearance to either cross or hold short of Runway 15L. TP 312, Aerodrome Standards and Recommended Practices also refers to TP2633, Manual of Airport Traffic Directives for the Operation of Vehicles on Airport Movement Areas and TP11465, Airport Safety Programs Manual. Both of these publications have been withdrawn. Although they are still used as a basis for individual AVOP programs at various airports, they were applicable only to airports that were owned or operated by Transport Canada. Transport Canada has formed a working group within the Canadian Aviation Regulation Advisory Committee (CARAC) to develop recommendations to ensure a more formal approach to airside vehicle activities. The NAV CANADA report9 also analyzed the available data and indicated the following: A direct correlation exists with traffic volume, and most incursions occur during daylight [visual flight rules] VFR conditions; Studies have shown that the highest accident potential is during IFR weather conditions or during periods of darkness; and Pilot deviations represent the highest number of reported incursion events, however, there is very little information collected from the pilots . . . to analyze performance or determine procedural deficiencies [of the air traffic control system]. The NAV CANADA report contained, inter alia, recommendations that: 7. airport authorities meet with Transport Canada to discuss an awareness program for airport vehicle operators. [Note: the Transport Canada report was silent as to an awareness program for AVOPs.] 8. a decision be made by NAV CANADA on the requirement for a standard national incursion warning system [as a defence against forgetfulness which is identified as the most common cause of runway incursions by controllers]. It notes that there is a wide range of alerting devices and memory aids already in place at different locations but that the effectiveness and usefulness of each should be re-evaluated. 14. ATC procedures be modified so that aircraft are not taxied into position on a runway if a delay for take-off clearance is anticipated. 18. authorization should be required for all aircraft/vehicles movements to cross runways, whether active or not. [Note: the Transport Canada report contained a similar recommendation with respect to aircraft but not vehicles.] 22. Airport authorities consider the installation of an inductive-loop system similar to the system in operation at Long Beach, California at high-risk airports. On 18 October 2001, NAV CANADA amended the Air Traffic Control Manual of Operations (ATC MANOPS) to require that aircraft and vehicles be instructed to either 'cross' or 'holdshort' of any runway it will cross while taxiing or operating on the airport manoeuvring area10. The taxi authorization given to Tractor197 did not contain the requisite instruction in accordance with this procedural change.